94 lines
4.1 KiB
Diff
94 lines
4.1 KiB
Diff
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From cdaf655f73bb3be10d47ab6f00d71a8d0b1a81e3 Mon Sep 17 00:00:00 2001
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From: Matthijs van Duin <matthijsvanduin@gmail.com>
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Date: Wed, 21 Jul 2021 11:10:36 +0200
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Subject: [PATCH] sd-bus: fix missing initializer in SD_BUS_VTABLE_END (#20253)
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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When two fields were added to the vtable.x.start struct, no initializers
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for these were added to SD_BUS_VTABLE_END which also (ab)used that
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struct (albeit sneakily by using non-designated initialization).
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While C tolerates this, C++ prohibits these missing initializers, and
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both g++ and clang++ will complain when using -Wextra.
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This patch gives SD_BUS_VTABLE_END its own case in the union and
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clarifies its initialization.
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I tested the behaviour of g++ 10.2 and clang 11 in various cases. Both will warn
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(-Wmissing-field-initializers, implied by -Wextra) if you provide initializers for some
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but not all fields of a struct. Declaring x.end as empty struct or using an empty initializer
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{} to initialize the union or one of its members is valid C++ but not C, although both gcc
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and clang accept it without warning (even at -Wall -Wextra -std=c90/c++11) unless you
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use -pedantic (which requires -std=c99/c++2a to support designated initializers).
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Interestingly, .x = { .start = { 0, 0, NULL } } is the only initializer I found for the union
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(among candidates for SD_BUS_VTABLE_END) where gcc doesn't zero-fill it entirely
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when allocated on stack, it looked like it did in all other cases (I only examined this on
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32-bit arm). clang always seems to initialize all bytes of the union.
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[zjs: test case:
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$ cat vtable-test.cc
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#include "sd-bus.h"
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const sd_bus_vtable vtable[] = {
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SD_BUS_VTABLE_END
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};
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$ g++ -I src/systemd/ -Wall -Wmissing-field-initializers -c vtable-test.cc
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vtable-test.cc:5:1: warning: missing initializer for member ‘sd_bus_vtable::<unnamed union>::<unnamed struct>::features’ [-Wmissing-field-initializers]
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5 | };
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| ^
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vtable-test.cc:5:1: warning: missing initializer for member ‘sd_bus_vtable::<unnamed union>::<unnamed struct>::vtable_format_reference’ [-Wmissing-field-initializers]
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$ clang++ -I src/systemd/ -Wmissing-field-initializers -c vtable-test.cc
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vtable-test.cc:4:4: warning: missing field 'features' initializer [-Wmissing-field-initializers]
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SD_BUS_VTABLE_END
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^
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src/systemd/sd-bus-vtable.h:188:28: note: expanded from macro 'SD_BUS_VTABLE_END'
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.x = { { 0 } }, \
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^
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1 warning generated.
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Both warnings are gone with the patch.]
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(cherry picked from commit 654eaa403070d3c897454a5190603fda4071c3ff)
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Conflict:NA
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Reference:https://github.com/systemd/systemd/commit/cdaf655f73bb3be10d47ab6f00d71a8d0b1a81e3
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---
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src/systemd/sd-bus-vtable.h | 9 ++++++++-
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1 file changed, 8 insertions(+), 1 deletion(-)
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diff --git a/src/systemd/sd-bus-vtable.h b/src/systemd/sd-bus-vtable.h
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index 75f8848360..35c942b16c 100644
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--- a/src/systemd/sd-bus-vtable.h
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+++ b/src/systemd/sd-bus-vtable.h
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@@ -75,6 +75,9 @@ struct sd_bus_vtable {
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uint64_t features;
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const unsigned *vtable_format_reference;
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} start;
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+ struct {
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+ size_t reserved;
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+ } end;
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struct {
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const char *member;
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const char *signature;
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@@ -185,7 +188,11 @@ struct sd_bus_vtable {
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{ \
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.type = _SD_BUS_VTABLE_END, \
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.flags = 0, \
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- .x = { { 0 } }, \
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+ .x = { \
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+ .end = { \
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+ .reserved = 0, \
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+ }, \
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+ }, \
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}
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#define _SD_ECHO(X) X
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--
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2.33.0
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